Cleaning compositions of various types have been known for many years, comprising many different components. Such composition are used to solubilize, abrade, oxidize, or reduce surfaces in an effort to remove undesirable surface adherents and restore a desired surface. Each type of surface to be cleaned presents its own characteristics which must be taken into account when choosing an appropriate cleaning composition therefor. Polymeric substrates offer particularly problematic issues in choice of cleanser composition due to the relatively large amounts of proteins which adhere thereto.
Especially thorny cleaning problems arise when the substrate to be cleaned is a contact lens. In addition to the parameters to be considered for the polymeric material of the contact lens per se, one must also take into account that the optical surfaces cannot be scarred, residue must be quickly and easily rinsed away with very small volumes of fluid, tonicity must be in an appropriate range so as not to destabilize the material, the cleaning system has to be non-toxic and non-allergenic (at least to the extent residue remains or is likely to remain) etc.
Specifically with reference to contact lens cleaning, protein adhesion and build up on the lens, sequestered primarily from tear fluid, has been a persistant and nagging problem. To deal with this difficulty, three general approaches have been attempted. The earliest attempt was to include an abrasive component, so that upon rubbing the lens therewith, the adhering protein would be broken up and town away from the lens. Compositions of this type include slurries of organic compounds such as sucrose, dextrose, etc., of inorganic compounds such as silica, sodium chloride, aluminum oxide, sodium carbonate, etc., of polymeric materials such as nylon beads, silicon polymer beads etc., or of other particulate matter such as glass beads.
A second type of attempted solution involved adding a surfactant. The surfactant is added to substantially solubilize the adherent protein. Compositions of this type include siloxane surfactants, alkylglycosides, polyalkylene oxy modified silicone etc. Attempts were also made in the combination of the two types above. Such compositions include Opticlean and Restore.
A third type of attempt to deal with the adherent protein has been to utilize an enzyme to digest the protein.
Of course the protein method can be used alone or in combination with any of the aforementioned methods of dealing with protein deposits. Typical available enzymatic cleaners for contact lenses include papain, subtilisin, pancreatin and other proteases.
While each of these methods has been somewhat successful in protein removal, each presents its share of drawbacks. For example, many abrasives are too harsh for use with contact lenses. Surfactants, in efficacious amounts for their surfactant properties, can irritate the eye terribly. Enzymes which degrade protein must never be placed into the eye for obvious reasons. Furthermore, the smaller protein fragments which result may be taken up further by the lens material or penetrate deeper into the lens matrix. In addition, enzymes if injected into the environment in substantial quantities create a considerable environmental hazard.